Nitration



Sept. 11, 1934. I B K BROWN I 1,973,559

NITRATION Filed July 15, 195s big/droom' INVENTOR BAM-Qi.

G15/Carige;

Patented Sept. 11, 1934 i unirse stares Pars-NT oFFlcs 1,973,559' Ni'mA'rioN I Bruce K. Brown, l/l-Iilmette,l Ill.; assigner to Standard Oil Company, lChicago, I1l., -a )corporation of llruiana` l Application July 13V,- 1933,-Scrial`No.`680,26 0

is oral-rms., (ergst-.144)

This invention relates to nitration processes reaction Vessel is getting out of control, the Whole and it'comprises processes `wherein liquid poly- Charge is dumped into a large Volume of Water hydroxy compounds, such as glycerine, the 4maintained,in'a tank ben'eaththe reaction vessel. glycol's, polymerized glycerine, glyceryl mono- Temperature control i's thus perhaps the most s chlorhydrin, and liquid mixturesY thereof'with important'single factor in nitroglycerine manu- 60 sugar, are nitrated to form nitro compounds such facture and, as stated' above, this control has as nitroglycerine, nitroglycols, and'nitrated soluf hitherto been accomplished by the use of brine tions of carbohydrates in the glycerine, the proc# coils 'in'the nitraton by the rate of adding the ess being characterized by nitrating in intimate glycerine, and by'agitation. contact with a relatively low-boiling hydrocarbon I have now been able to simplify and improve 65 Which acts as an internal, direct-contact coolingr temperature control in this art to such an extent medium to absorb the eat of the reaction and that I can markedly increase the rate of adding to keepthe reaction temperature within limits the glyeer'in'e tov themixed acids and thus in-A of safety and high yields. creasev the production rate. I have been able In the customary methods of making nitroto operate at slightly higher nitration tempera- 70 glycerine, and similar nitro compoundssuch as tures Withoutjincreasing'side reactions; and With nitrated glycols, and the like, many precautions an entire avoidance of local overheating, I have are taken to insure safety of operation. It is been able to make a nitroglycerine requiring less not at all unusual to nitrate several hundred extensivejpurication to free it ofoccluded acids. pounds of glycerine in a single charge, this yield- I have found that the heat of the reaction 75 ing as much as 1500 pounds of nitroglycerine. can be absorbed bythe use of loW boiling hydro- It has long been appreciated that the tempera- 'carbons directly mixed in with the mixture of ture of the reaction must be under continuous, glycerine and acids and, provided an appropriate accurate control. This temperature is generally choice of hydrocarbons, or mixtures thereof, is

y,25 from 22 to 25 C.` and extreme care is' taken exercised,'I'can control the temperature of the 80 to insure that the temperature does not Aexceed reaction mixture at all times and such control this limit. Control of the reaction is Vusually is entirely automatic `so long as hydrocarbon is accomplished by providing the reaction vessel retained in the mixture. ATo put it another Way, with brine coils and running the glycerine into I utilize asrcooling agents, either alone, or in the mixed acids very slowly. Agitation is con conjunction with the customary brine coils, hy- 85 tinuous and, in this country, agitation is by drocarbons having boiling points, or high vapor mechanical means. The agitator is operated by pressures, 'Within the permissible temperature a small steam engine and means are also prorange of the reaction. Ihese hydrocarbons are vided to run the agitator by man power in case mixed' with` the glycerine and acid-s. Should the steam fails. Electric motors, are of course, localized heating develop during the course of 90 excluded because of the danger of sparks in the the reaction' some of the hydrocarbon is immevicinity of the nitro-glycerine. Agitation is for diatelyfvolatilized, thus absorbing the heat, and the purpose of mixing the glycerine with the the overheating checked before it has had any acids but is also essential to prevent localized 'opportunity'to exceed limits of safety.

40 overheating. As the glycerine runs into the Generallyluse saturated aliphatic hydrocar- 95 mixed acid, reaction starts immediately on the bons; for example, normal pentane, boiling point surface of each globule of glycerine and the 38 C., isopentane, boiling point 30 C., butane, heat liberated is quite considerable. This heat boiling point 1 C., and other hydrocarbons, or must be dissipated as quickly as possible, othermixtures thereof as will be more fully explained'.

Wise it may increase to the danger limit and Itis best to use saturated aliphatic hydrocarbons 100 a whole charge of nitroglycerine may beexploded Since these have A'absolutely no Atendency to react because of localized heating in a relatively small With'the mixed acids atthe low temperatures of portion of the mixture. The decomposition of the nitration'reaction. My invention, however, is the nitroglycerine is greatly accelerated by the broad enough to include hydrocarbons other than 5o presence of the acids. Acid-free` nitroglycerine those of the'saturated aliphatic series provided 105 is' much less sensitive to moderately elevated thehydrocarb'on chosen does not, at'25 C. to temperatures. The experienced` nitroglycerine 30 C., orV below., show anymarked tendency to man recognizes rapid, dangerous decomposition', read? With 1711 S'IOrlg miXed acids. by the formation of fumes of red oxides of nitro# Nitroglycerine is but slightly soluble in hydrogen. When it appears that the charge in the carbon solvents.` Generallythis-solubilityisof the 1,10

' advantage inmy process since practically all of the ntroglycerinemay be readilyfseparated from the hydrocarbon cooling agent by kallowing they ymixture to stratify. The hydrocarbon layer, containing a small quantity ofy nitroglycerine, is, after 'separation from rthe rnitroglycerine layer, returned to the reaction vessel as will be described.

Onthe appended singley sheet of drawing I have illustrated my processes adapted tothe manufacture of nitro compounds such as nitroglycerine,

f nitroglycols, i nit'ratedy polymerized glycerine, ni-

trated mixtures of glycerine andsugar and nitrated chlorhydrin derivatives of glycerine. The

manufacturing 'operations inr making all of f these compounds are almost identical and it will su'ce if I refer to them broadly yas nitroglycerine manufacturing operations; f yThe following description f is thereforenot` restricted to nitroglycerinefper se.r A nitration kettle 1,'isy provided with the usual brine coils2, yagitatorr 3r and thermometer well 4, f containing thermometer 5. i Mixed racids r(nitricy rand sulphur-ic) are charged in rat 6 and glycerine at 7. rDump outlet and valve 8 isalso providedr at the bottomof the kettle. i Inlet 9 is forthe'purf pose koi introducingl hydrocarbon lcooling agenty f and through outlet rand rvalve 10 rthe contents of the'kettle' may be conveyed to a separator 'llfby yfvvayoi line 12. 30`

' from kettle throughfli'ney 13,y valve 14, condenser' coil y15 immersed in cooling bath 16 and' thence i return-ing'the hydrocarbon to intermediate stori age tank 17 which may be vented at 18 for the ref' f Cooling is obtained by evaporat- -ing a portion ofthe hydrocarbon cooling agent moval of uncondensible gases. Brine coils' 2in1- i rush` auxiliary ycooling, if required.y f yIf desired, kettle 1 can be operated under a slight-vacuum: by f means of compressor 19. In this caser valve 2o ywill be closed 'and valves r21 and 22 opened.l f

`'Beneath thereaction kettle emergency dump Atank 15 is provided as usual in this art. This tank is always filled with Water.

After the nitration is finished, the contents of vthe reaction kettle are conducted to separator 11 wherein the mixed acid, having a specic gravity of around 1.7 is separated from the upper layer of nitroglycerine. The acids are withdrawn through four-way valve 23 and sent to an after separation vessel, or to a recovery plant, by Way of line 24. The impure nitroglycerine iiows to a washing apparatus 25 by Way of line 26 and the upper hydrocarbon layer, having a specic gravity greatly less than the nitroglycerine, is drawn off through line 27 andpumped, by means of pump 28 and line 29 back to the nitrator or reaction kettle. The returned hydrocarbon contains but little dissolved nitroglycerine and hence no hazards are involved in pumping it. Alternatively, the hydrocarbon layer from separator 11 can be recycled back to storage tank 18 by means of line 30, pump 31 and line 32. When hydrocarbon is needed for another nitration it can be introduced into kettle 1 from tank 17 by means of line 32, pump 31, line l 30, pump 28, line 29 and inlet 9. Make-up hydrocarbon cooling agent can be supplied through pipe 33. This also serves as a quick and certain emergency method of introducing hydrocarbon for cooling purposes.

Separator 11 is also .provided with a reflux arrangement comprising line 34, condenser 35, separator 36 and return line 37 to reux and return any volatilized hydrocarbon. Vapors can be vthdrawn from separator 36 through valve 38 and passed through valves 21 and 20 or compressor 19 and valve 22 back to the'hydrocarbon recovery ywith the usual procedure. Ation is usually conducted at somewhat elevated f temperatures, around 40 C. so that, at this teml perature, any hydrocarbon retained inthe Lmixy'ture is rvolatilized out, advantageouslyy .under a,

system, thereby coolingfseparator 11. f It is desirable at thisy stage to keep therefrigerant in con-y tactwith the nitroglycerine since the nitroglyc- 'erine-in'contactwith theacid is still a dangerous substance.r When withdrawing nitroglycerine fromseparator 11 rto be conducted to washer 25,

it is best to Withdrawabout aithfud ofthe hydrof the nitroglycerine which has separated out goes to the Washer and none of it, other than that dissolved inthe hydrocarbon, is pumped back to ther reaction kettle. f f f f The separated nitroglycerine, together with the y f f f y y yhydrocarbon cooling agent passes to washer 25 and is washed with water' introduced through line This insures that all of f f f y 39;y A'reflux-arrangement comprising yline 40,

of rlinef47.r The ymiddleor water layer is run to f Waste or acid recovery through line 48 by means of three .Way valve 49, and they top orlhydrocarbon layer is then conducted back tothe reaction vessel through valve 49, pump 28, line 29 and inlety 9 -The nitroglycerine introduced into: Washery 46 is washed therein with duutesodium-carbonate f or bankto storage tank 18 bymeansof pump 3l.

solutionr introduced throughy line 58 in accordance yThis Washing operaslight vacuum, the vapors iowing through valve 59, line 50', pump 19 and valve 22, being condensed by condenser 16 and returning to tank 17. The bulk of the hydrocarbon passing on from Washer 46 may be condensed in condenser 51, separated from the vaporsI in separator 52 and returned to acids and glycerine, observing the usual ratios to give the best results. These depend upon purity of the glycerine and strength of the acids. For example, the ratios can be parts of glycerine, 300 parts of nitric acid of 93-94 percent monohydrate and 500 parts of sulfuric acid of 95 per- 1 cent monohydrate. The mixed acids, at a temperature of 20 C. or less are charged into reaction kettle 1. Y

I then introduce about 500 parts of a hydrocarbon mixture boiling at about 30 C. or having a high vapor pressure at 25 to 30 C. This is iive degrees higher than the usual permissible temperature limits. This hydrocarbon mixture may consist entirely of isopentane, or it may consist of a mixture of normal pentane and butano, or normal pentane alone (boiling point 38 C.) Although I prefer to use a hydrocarbon mixture boiling within the reaction temperatures chosen, I amrnot restricted to this. I can use hydrocarbons having high vapor pressures at these temso. f

Y C. lest the nitroglycerine be frozen.

peratures. stance After the hydrocarbon cooling agentl has been introduced, I advantageously flow cold brine through the cooling coils in the kettle. When I use the brine, my hydrocarbon internal refrigerant chiefly acts as a check to completely control the temperature and to prevent localized overheating. Less hydrocarbon can therefore be used. YAlternatively I can dispense entirely vwith a cooling coil andrely on the hydrocarbon for complete refrigeration.' In either case, I next start the agitating device and maintain cooling conditions by evaporating hydrocarbon through line 13, liquid hydrocarbon being returned'through inlet 9 Aas required to replace that evaporated. Then the glycerine is added slowly through inlet 6. I find that the glycerine can be added at a rate as much as fifty percent faster compared with ordinary processes because of the immediate chilling effect of the hydrocarbon refrigerant. Since the refrigerant is insoluble in the mixed acids, as is also the glycerine, all' substances in the reaction kettle are mixed together by the agitator sovthat a sort of coarse emulsion or suspension of glycerine and hydrocarbon exists within the vessel. This means that the refrigerant, or a heat absorbing material, is in direct contact withl glycerine at all times so that any localized overheating in the interior of the body of liquids remote from the cooling coils is at once corrected. This is a very important advantage. Moreover, volatilization of the hydrocarbon tends to stir the mixture and thus assists inV heat dissipation.

When hydrocarbon is used as the refrigerant alone, quantities of it are vaporized and refluxed. Care should naturally be taken that the rate of reflux is sufficient to return the hydrocarbon al- Normal pentane is one such subn most immediately. 4In this case, it will be observed that the hydrocarbon really acts as a most efficient heat transfer medium, heat being conducted from the reaction to the reflux cooling fluid and condensed, cold hydrocarbon being continuously returned to the reaction vessel.

When the hydrocarbon refrigerant is used in conjunction with the ordinary brine coils, the capacity of the reflux condenser need not be so great. In this case, as stated above, the hydrocarbon acts as a temperature control, most of the cooling being done by the brine coils. Localized overheating is entirely overcome, however, although the actual cooling action of the hydrocarbon is thus more or less limited to localized overheating. I can, of course, conduct the nitration at temperatures of 12.to 14 C. if desired, simply by an appropriate choice of hydrocarbons. For example I can use a mixture of tetra methyl methane,

' boiling at 9" C.and normal pentane. It is well known that lower nitration temperatures tend to lower side reactions .but care must vbe taken that the temperature does notget much below 12 I find it much more advantageous, however, to operate at usual nitration temperatures, generally 22 to 25 C.r or slightly higher because the reaction rate is increased.l As pointed-out above, one of the advantages'in my process isthat With inter'- nal automatic coolingvby means of volatile hydrocarbons' in direct contact with the reaction mixture the tendency for side reactions is greatly reduced. These side reactions while dependent to some extent upon the purity of the glycerine, are Vnevertheless materially increased as the temperature increases unless adequate means are 'taken to prevent localized overheating.

After vthe nitration is finished, the nitroglycerine is purified in the usual way by washing with water and then with dilute sodium carbonate solution. My invention does not materially change these operations. I do, however, nd that the nitroglycerine separates Vmore rapidly, and cleaner, fromthe acid layer. v'This may in part be attributed to the fact that side reaction products are greatly lessened. Recovery of the hydrocarbon cooling agent involves no dimculties. Most of it is recovered as a liquid immiscible with the nitroglycerine layer. Small quantities of hydrocarbon iiowing to the alkali washing apparatus are readily removed by distillation since the usual temperature in this stage is 40 C. or slightly higher. This is high enough to volatilize off any remaining hydrocarbon.

While I have more specifically described my process in relation to the manufacture of nitroglycerine, it will be obvious that the process steps are identical when making nitroglycols, when nitrating polymerized glycerine, and when nitrating various mixtures of glycerine and sugar. The only changes necessary are those connected with the ratios of mixed acids to material to be nitrated. These ratios are, however, Well known in the art. In fact, my .process does not modify ordinary nitroglycerine*technique in any way other than in the cooling and temperature control of the nitration reaction.

In a modification of the above processes, I can conduct the nitration of glycerine under pressures slightly in excess of atmospheric. This is sometimes an advantage. For instance, I can use butane as the 'hydrocarbon cooling agent and conduct the nitration under a pressure of about 31 pounds per square inch absolute.` At this pressure, the butane boils at about 20 C. a desirable'nitration temperature. Butane alone cannot be used at atmospheric pressure when nitrating glycerine because its low boiling point, 1 C. would tend to freeze the nitroglycerine. In such cases, it is desirable to operate under pressures above atmospheric so as to increase the boiling point of the hydrocarbon. Y0n the other hand', the nitroglycols have very low freezing points, considerably below 1! C. so that when nitrating glycols I can use butane as the cooling agent at Vordinary atmospheric pressure.

In general; I correlate the hydrocarbon cooling agents, or mixtures thereof, with the pressure and the desired operating temperature so that, at any temperature above the nitration temperature, volatilization of the hydrocarbon takes place. It will, of course, be understood that the latent heat of vaporization of the hydrocarbons is relatively great-so that `very large quantities of 4heat are labstracted from the reaction mixture.

Alternatively, I can operate at pressures below atmospheric. This is desirablewhen, for economic reasons, such as availability of the hydrocarbon cooling agent, it is necessary to use normal pentane, or even hexane alone. Both of these substances have boiling pointshigher than normal nitration temperatures.Y By nitrating Linder reduced pressure, the boiling points arelowered. Normal pentane, for instancalboils at 25 C.`un der an absolute pressure of 9 pounds per square inch. I-Iere again I am correlating the hydrocarbon with the pressure and desired nitrating Mil' ISD

temperature so 'that the hydrocarbon boils at the nitrating temperature. l

Although the somewhat elaborate system of recovering and recycling my hydrocarbon cooling agent as shown in the drawing is generally advantageous, to secure good control and adequate refrigeration, it is possible to simplify theapparatus by substituting ordinary reflux condensers above kettle 1, separator 11, washer 25, etc.

What is claimed is: .y

1. .The processV of low temperature nitration of. liquid aliphatic dihydroxy and polyhydroxy compounds of the glycol, and glycerine class which includes nitrating the hydroxy compound while admixed with a hydrocarbon in the liquid state, said hydrocarbon being unreactive Awith the nitrating acid at the temperature of the nitration and having a high vapor pressure at the temperature of the nitration, the hydrocarbon acting to control the `nitration temperature by absorbing reaction heat and volatilizing.

2. The process of low temperature lnitration of liquid aliphatic dihydroxy and polyhydroxy compounds of the glycol, and glycerine class J; whichincludes nitrating the hydroxy compound under pressure While admixed with a hydrocarbon in the liquid state, said hydrocarbon being unreactive with the nitrating vacid at the tempera-l ture of the nitration and having a boiling point j at atmospheric pressure less than the ltemperature of the nitration, the pressure, during the nitration, being suiiicient to retain the hydrocarbon in the liquidv state at the nitration telnperature but permitting it V-to volatilize on an j increase in temperature whereby the hydrocarbon acts to control the nitrationtemperature by absorbing reaction heat and volatilizing. Y

3. The process of low temperature nitration of liquid aliphatic dihydroxy and polyhydroxy j compounds of the glycol, and glycerine. class which includes nitrating `the hydroxy compound under a pressure less than atmospheric while adrnixed with a hydrocarbon in the liquid state, said hydrocarbon being lunreactive with. the nis; trating acid at the temperature of the nitration and having a boiling point at atmospheric pressure greater than the temperature of the nitration, the pressure, during nitration beingsuch that the hydrocarbon is retained in the liquid state at the l nitration temperature but permitting it to volatilize on an increasein temperature whereby the hydrocarbon acts to control the nitration ternperature by absorbing reaction heat Vandvolatilizing. A Y.

4. The processas in claim 1 wherein theA volatilized hydrocarbon is continuously condensed and returned to the mixture undergoing nitra tion.

5. The process as' in claim 2 wherein the `vola- -tilized hydrocarbon is `continuously condensed and returned to the mixture undergoing nitration.

6. The process as in claim 3 wherein the'volatilized hydrocarbon is continuously condensed and returned tothe mixture undergoing nitration. l

7. The process asin claim Y1 wherein the hydrocarbon is a saturated aliphatic hydrocarbon,

3. The process as in claim 2 wherein the hydro- I carbon is a saturatedaliphatic hydrocarbon.

Y10. The processasin claim 1 wherein the temperature of vthe reaction mixture is additionally controlledby cooling coils arranged therein.

11. The process as in claim 2 wherein the temperature of thereaction mixture is additionally controlled by cooling coils arranged therein.

12. The process as in claim 3 wherein the temperature of the reaction mixture is additionally controlled by cooling coils .arranged therein.

13. The process oflowtemperature nitration of liquid aliphatic dihydroxy and polyhydroxy compounds of the glycol and glycerine Vclass which includes nitrating the hydroxy compound at a temperature of C. to 30 C. while admixed with a hydrocarbon in the liquid state, said hydrocarbon being unreactive with the nitrating acid at the nitrating temperature and having a high vapor pressure at this temperature, continuously condensing and returning volatilized hydrocarbon to the reaction mixture, separating the quantities of hydroxy compounds, and washing and neutralizing thenitro compounds.

14. The process as in claim 13 wherein the nitration is conducted under a pressure in excess of atmospheric and the hydrocarbon used has a boiling vpoint at atmospheric pressurefless than the temperature of `theV nitration, the pressure during nitration being sufficient -to retain the hydrocarbon in the liquid state at the temperature of the nitrationY but permitting it to volatilize on anV increase in temperature.

15. yThe process as in claim 13 wherein the nitration is;conducted under a pressure less than atmospheric andthe hydrocarbon used has a boiling point at atmospheric pressure greater than the temperature of the nitration, the pressure during nitration being such that the hydrocarbon is retained in the liquid state but permitting it to volatilize on an increase in temperature.

16. The process as in claim 13 wherein the temperature of the reaction is additionally controlled by cooling coils therein.k

17. The process of low temperature nitration of liquid aliphatic dihydroxy and polyhydroxy compounds of v the glycol and glycerine class which includes nitrating the hydroxy compound at a'temperature of 20 C. to 30 C. while admixed with a hydrocarbon in the liquid state, said hydrocarbon being unreactive with the nitrating acid. at the nitrating temperature and having a high vapor pressure at this temperature, continuously condensing and returning volatilized hydrocarbon to the reactionmixture, separating the acid, after. completion of the nitration, from the reaction products, separating most, but not all, of the hydrocarbon from the reaction products and returning the separated hydrocarbon for re-use in the nitration of-furtherquantities of hydroxy compounds, washing'the nitro Vcompounds and remaining hydrocarbon with Water, separating the hydrocarbonl from thewash water and nitro compounds and returning. the Yhydrocarbon for re-use, and finally washing the nitro .compounds with. dilute alkali to remove traces of acid.

18; The process as in claim 1'7 wherein the temperature of reaction is additionally controlled by L cooling coils therein. l Y

v BRUCEK. BROWN. 

